1. Field of the Invention
The invention generally relates to a digital color camera and is directed more particularly to a digital color camera which produces an output from an imager which is digitally processed so as to provide a digital color television signal.
2. Description of the Prior Art
A digital color camera adapted to digitally process an output produced by an imager so as to provide a digital color television signal is greatly improved in signal processing, circuit arrangement, and reliability as compared to a color camera in which the color television signal is processed in analog fashion over its entire signal processing interval. Recently, for this reason, almost all of the signal processings in a color camera are being performed in digital fashion.
In the prior art when the output signal is digitally processed so as to form the color television signal, the processing rate has been selected to be a frequency which is three or four times higher than the color subcarrier frequency f.sub.sc. This is mainly because of the ease of signal processings, for example, and ease of modulation.
In general, a color signal has a band width from 0 to 4 MHz. However, a person can discriminate a color of a pattern with a relatively large area or a band width of the television signal from 0 up to 0.5 MHz, but a person cannot discriminate a color of a fine picture image with a band width of 0.5 to 4 MHz. Accordingly, it is normal for the color signal to be limited in bandwidth so as not to cause problems in practice and to thereby obtain ease of transmission.
In digital processing, the bandwidth is limited with a digital filter of, for example, a non-recursive or FIR (finite impulse response) type.
It is known with a digital filter that as the ratio f.sub.c /f.sub.s (where letter f.sub.c represents a cutoff frequency, for example, 800 kHz and f.sub.s represents its driving clock frequency or sampling frequency) becomes smaller, the transfer function becomes more complex and hence the number of orders has to be increased or raised and thus the circuit arrangement of the filter becomes complex. In the prior art, since f.sub.s has been selected as three or four times the color subcarrier frequency f.sub.sc (which is, for example, from 10.74 MHz to 14.3 MHz), the ratio f.sub.c /f.sub.s is reduced. As a result, the arrangement of the digital filter becomes quite complex which is undesirable.
U.S. Pat. No. 4,069,501 which issued on Jan. 17, 1978, reissued as U.S. Pat. No. Re 30,800 on Nov. 17, 1981 invented by the applicant discloses techniques for eliminating aliasing noise by spatially offsetting the CCD picture elements.